Advances in directional drilling techniques enable the path of a subterranean borehole to be precisely routed in a manner that maximizes oil production. Measurement-while drilling (MWD) and logging-while-drilling (LWD) techniques provide, in substantially real-time, information about a subterranean formation as a borehole is drilled. Such information may be utilized in making steering decisions for subsequent drilling of the borehole. For example, an essentially horizontal section of a borehole may be routed through a thin oil bearing layer. Due to the dips and faults that may occur in the various layers that make up the strata, the drill bit may sporadically exit the thin oil-bearing layer and enter nonproductive zones during drilling. In attempting to steer the drill bit back into the oil-bearing layer, an operator typically needs to know in which direction to turn the drill bit (e.g., up, down, left, or right). In order to make correct steering decisions, information about the strata, such as the dip and strike angles of the boundaries of the oil-bearing layer, is generally required. Such information may be obtained from azimuthally sensitive measurements of electrical properties (e.g., resistivity and dielectric constant) of the surrounding subterranean formation.
Azimuthally sensitivity MWD/LWD resistivity tools are disclosed in the prior art. However, the precision demanded by directional drilling operations tends to require improved accuracy, increased angular resolution, and increased usability in all types of drilling fluids (also referred to herein as drilling mud). Areas of further potential improvement may include improved methods of tool manufacture, increased reliability, and/or lower cost than presently available with conventional resistivity tools. Therefore, there exists a need for improved azimuthally sensitive electromagnetic measurement tools suitable for LWD and/or directional drilling applications.